Energy efficient engines of reduced size are desirable for fuel economy and cost reduction. Smaller engines provide less torque than larger engines. To increase the torque capacity available from smaller engines, boosting systems have been developed for boosting the air pressure at the engine intake to increase the torque available from the engine. Conventional boosting systems can include superchargers and/or turbochargers. A turbocharger typically includes a first turbine exposed to engine exhaust flow and a second turbine positioned in the air intake of the engine. Exhaust flow from the engine turns the first turbine which transfers torque to the second turbine causing the second turbine to boost the intake air pressure. Turbochargers can be efficient but have the disadvantage of lag. Lag relates to a delay in providing boost pressure. Because the turbocharger depends on energy from the exhaust to provide the boost pressure, when the engine is operating at slow speeds, high levels of boost cannot be immediately provided when needed by the engine. Instead, full levels of boost are not provided until the engine reaches a high enough speed where the exhaust has sufficient energy to adequately drive the turbocharger. In contrast to turbochargers, superchargers are driven by torque drawn directly from the engine. This is advantageous because superchargers can provide a rapid boost in pressure without the type of delays associated with turbochargers. However, superchargers are typically designed with a fixed gear ratio that under normal driving conditions generates excess air flow that is typically routed through a bypass and recirculated through the supercharger. This results in energy loss. To overcome the above issues, boost systems have been developed that include both turbochargers and superchargers. In this type of boost system, the turbocharger can be designed taking efficiency primarily into consideration, and the supercharger can be designed to supplement the turbocharger to compensate for turbocharger lag.